The treatment of subterranean formations penetrated by a wellbore with fracturing fluids to stimulate the production of hydrocarbons is well-established. In general, such treatments are conducted by injecting a liquid, gas, or two-phase fluid down the wellbore at sufficient pressure and flow rate to fracture the subterranean formation. A proppant material, such as sand, fine gravel, sintered bauxite, glass beads, or the like, may also be introduced into the fractures to keep the fractures open after the fracturing pressure is released. Propped fractures provide larger flow channels through which an increased quantity of a hydrocarbon may flow, thereby increasing the productivity rate of the well. Fracturing operations may be combined with gravel packing operations in a technique known as frac-packing, which combined operations are designed provide both a barrier to formation sand production as well as proppant flowback.
Fracturing fluids generally include a gel comprising a gelling agent and a crosslinker, such gels providing useful rheological properties for fracturing. The rheological requirements of a fracturing fluid are subject to numerous design considerations. First, the fracturing fluid should have rheological characteristics that permit it to be pumped down the wellbore without excessive difficulty or pressure drop friction losses. In order to adequately propagate fractures in the subterranean formation, a fracturing fluid should provide sufficient viscosity to fracture the target interval and maintain sufficient fracture width to admit proppant. The fracturing fluid is also expected to provide sufficient viscosity to transport and deposit the proppant into the cracks in the formation formed during fracturing. During non frac-packing operations, the ideal fracturing fluids may optionally exhibit a low leakage rate into the formation during the fracturing operation. Finally, the fracturing fluid is also ideally designed to reduce in viscosity following fracture placement and readily flow back into the wellbore after the fracturing is complete, leaving minimal residue that could impair permeability and productivity of the formation.
In order to improve removal of the fracturing fluid after the fracturing operation, chemical additives are typically employed to “break” the fluid viscosity, which may include oxidizing agent chemicals or enzymes. Such reagents are typically designed to react with the gelling agent (polymer) portion of a gel, while the crosslinker is merely a spectator. However, with the complicated cooldown-profile during fracturing treatments, and the spectrum of temperatures at various depths into the fracture, chemical breakers must be carefully metered for varying concentration to be used at various times within a fracturing stage. Additionally, many chemical breakers have limited abilities to control the rate of breaking leading to frequent premature-breaking of the fluid and service quality issues in field operations. Premature break of the fluid with current chemical breaker technologies may lead to premature “screen-out” of the fracturing treatment, leading to stalled growth of the fracture geometry, reduced fracture penetration into the formation, and ultimately reduced hydrocarbon productivity of the fracture.